Lucas was called to the bar, Lincoln's Inn, on 30 April 1885. He became a civil servant in the Colonial Office which led to his becoming head of the Dominion Department and, in 1907, to his knighthood.
In the 1880s he was invited to teach at The Working Men’s College. From 1897-1903 he became Vice Principal of the College, and from 1912-1922 the Principal.
He wrote ‘A Historical Geography Of The British Colonies’ (1908),A History of Canada: 1763-1812 (1909) ‘The Canadian War of 1812’, and ‘The Partition’ (Clarendon Press 1922).